Wave generating system



Oct. 21, 1498 A. c. LUTHER, JR 2,857,514

WAVE GENERATING SYSTEM INFENTOR.

A. C. LUTHER, JR

WAVE GENERATING SYSTEMv 4 Sheets-Sheet 2 QcLZl, 1958 Y l 'fz S710/#MMM Pl/l SES Fi'ied oct. so, 195s S26/wu l r 007907' INI/ENTOR.

Oct. 21, 1958 A. c. LUTHER, JR

WAVE GENERATING SYSTEM 4 Sheets-Sheet 5 Filedl 001;. 30, 1953 ATTORNEY oct. 21, 195s A. c. LUTHER, JR

WAVE GENERATING SYSTEM 4 Sheets-Sheet 4 Filed Oct. 30,'1953 km SAN mwN NNN Q\\ j NQ@ United States Patent O WAVE GENERATIN G SYSTEM Arch C. Luther, Jr., Merchantville, N. J., assignor to Radio Corporation of America, a corporation of Delaware Application October 30, 1953, Serial No. 389,312

12 Claims. (Cl. Z50-27) The present invention relates to improvements in signal generating systems and more particularly, although not necessarily exclusively, to wave generatingsystems which employ multivibrator type signal generating means.

In a more specific sense the present invention relates to improvements in multivibrator signal generating systems particularly of the monostable type, and especially concerns itself with improvements in the operation of monostable multivibrator circuits in their application to television synchronizing and blanking waveform synthesis.

In the art of electrical signal communication it is commonplace to employ multivibrator signal generating means to aid in the synthesis of complex waveforms. Multivibrators as a class of electrical circuit fall into several prominent categories or types. A multivibrator circuit is generally based upon what may be considered two distinct amplifying means having their input and output circuits connected to one another in a regenerative relationship. Depending upon the type of the multivibrator, one or more time constant circuits are included in the regenerative connection of the two amplifying means whereby to cause the generation of waveform having pulse components whose duration is defined by the time constant circuits employed.

Multivibrator circuits which sustain a continuous development of signal waveforms are usually referred to as astable multivibrators and as such are frequently thought of as free-running multivibrator-s. A second class of multivibrators known as monostable, provide an output waveform only when triggered by a control pulse, the duration of the output waveform, of course, depending upon the time constant characteristic of the circuit included in the associated time constant circuit. In monostable multivibrators the circuitldisplays a normal or rest condition in which a predetermined one of the two amplifying means remains in an operating state. A third type of multivibrators known as bistable involves circuitry which permits the circuit to rest with either amplifying means in a conducting state. Application of control pulses to such a circuit merely transfers the rest condition to the other amplifying means. This latter type of multivibrator circuit is commonly referred to as a dip-flop circuit.

The present invention concerns itself with means for controlling the timing of a multivibrator during its operation whereby to produce an output signal of controllably different widths. By applying the novel features of the present invention to monostable multivibrator circuits, it is possible to produce exceedingly complex output waveforms having pulse components covering a wide range of width and frequency.

In one particular embodiment of the present invention a single multivibrator circuit of the monostable type may be supplemented with novel control means which will permit the direct development of R. T. M. A. television synchronizing and blankng waveforms. Such an a1'- rangement Provides an exceedingly accurate means for 2,857,514 n Patented Oct. 2 1, 1958 2;- developing a waveform heretofore requiring considerable apparatus of a bulky and costly nature.

It is, therefore, an 4object of the present invention to provide an improved signal generating system in which the character of the developed signal may be conditionally varied in accordance with a predetermined pattern during the generation thereof.

It is another object of the present invention to provide an improved multivibrator circuit having timing characteristics which are controllable by signal responsive means so as to permit the character of the developed output signal to be methodically controlled during its generation.

It is further an object of thel present invention to provide an improved monostable multivibrator circuit having associated therewith timing control means whereby both the frequencyandduration of pulse components produced by the multivibrator are controllable in response to signal intelligence.

It is yet another objectl ofthe present invention to provide a simple, economical and accurate system ncorporating multivibrator Waveform generating means which will directly synthesize complex signal waveforms having pulse components of different frequency and different durations.

It is still another object of the present invention to provide a simple and Vimproved signal generating means for producing the blanking, synchronizing, equalizing and vertical serration elements of a standard R. T. M. A. television signal.

In the realization of the above objects and features of advantage, the presentinvention takes advantage of the fact that a timing of the multivibrator circuit, especially of the monostable type, depends upon the value of the time constant circuit Vemployed therein as well as the degree or magnitude of charge imposed upon kthe time constant circuit at the'early portion of its wave generating cycle. In a preferred form of the present invention, the degree of charge or amount of charge imposed upon the time constant circuit is controlled by changing the effectiveness of that amplifying means in the multivibrator circuit connected in charging relation to the time constant circuit, per se. 'I'his control is preferably effected on a preset basis and at a time when the amplifying means of the charging sectionis inoperative. That portion of the multivibrator circuit designated to charge the time constant circuit will hereinafter be referred to as the charging portion of the multivibrator, while that portion of v the multivibrator circuit which responds to the charge applied to the time constant circuit will be referred to as the charge responsive portion.

It is furtherrwithin thescope of the present invention to provide means for not only controlling the effectiveness of the charging portion of the multivibrator circuit, but also to provide means for controlling the response characteristics of the charge responsive portion of the multivibrator circuit to the charge imposed on the time constant portion or means. Undesirable circuit transients which may, in some instances, accompany changes in the time constant circuit value and response characteristics of the charge responsive section of the multivibrator may, of course, be obviated through the above mentioned preferred form of the invention which provides control only of the charging section of the multivibrator circuit.

A more complete understanding of the operation of the present invention as well as other objects and features of advantage will be obtained through a reading'of the following specification, especially when taken in connection with'the accompanying drawings, in which:

Figure 1 is a block diagram representation of one basic form ofthepresentinvention illustrative of its operating principles.

Figure 2 is a combination block and schematic representation of still another form of the present invention.

Figure 3 is a graphical representation of certain waveforms capable of development by the embodiment of the present invention showninFi-gurc 2.

Figure 4 is a combination block and Vschematic representationf of a television synchronizing signal generator circuit embodying they novel features of the present invention. V V

Figure 5 is a graphical representationY ofr a television signalwaveform intime relation toother signal waveforms developed` by the: circuitry of Figure y4 employed to synthesize the synchronizing signal waveform section of the overall television signal. Y

, Turning now to Figure l,. there isv illustrated by the blocks 10, 12,14and 16 the-basic components of a multivibrator circuit. The chargingfamplifier devicel is connected to operate upon ai time constant circuit 12 whose output terminal is connected with a charge responsive amplifier device 14.l The'outputsignal from the amplifier device 14 is in turnlcoupledvia the signal coupling means 16 to the charging.` ampliler device 10. The components4 shown are representative of a monostable type multivibrator although by` placing a time constant means within the signal' coupling means 16, astable multivibrator action'may be achieved. Moreover, by adjusting the input circuit characteristics to the arnpliiier devices 10 and 14, bistablev multivibrator koperation maybe realized. The present invention, however, is more directly concerned with the operation of the elements s hown in amonostable mode and the discussion to follow hereinafter will be directed mainly toj the' consideration of monostable multivibrator operation. V It will -be understood, however, that the-basic principles of the present invention which will become hereinafter more apparent, are applicable to astable and bistable multivibrator operation. p y n If the basic multivibrator circuit ,comprisingthe elements shown in Figure l is considered to' rest with the charge responsive amplifier device 14 in a relatively con'-v ductive condition andthe charging amplicrdevice- 10 in a relatively non-conductive condition, it will be immediately apparentv that triggeringinto Aa relative non'- conductive state of the 4charge responsivevamplifler 14 will cause cycling of the multivibrator which will produce an output signal at terminal L18- having-ja pulse component Whose duration will be a function-'of the value of the time constant circuit-12. A s is well known inthe multivibrator art, the function ofthe' time const antcircuit 1,2v

is to maintain the charge responsiveV ampllier. device 14 in a relatively non-conducting. state for the duration of the multivibrator timing cycle` The eifectiveness of the time constant circuit 12 to do this will depend upon first,

i the amount of charge it has received from thercharging amplifier 10 and the responseA characteristics of the amplifier device 14. Thus, reducing the gain or mutual conductan'ce of the charging amplifier device 10v will reduce the amount of energy applied to the time constant circuit 12, and hence decrease the timing interval of the multivibrator'. Cori'espondingly, adjusting the operating potential of the ar'n'r'alitiery device 14' so that' it rests in a condition nearer conduction will cause the timing interval of the multivibrator" to be redi'iced for a given value of time constant circuit and a givencharge thereon.

The present invention, therefore, contemplates the provision of control means 20,' 22 and 24 which may be made responsive to' a control signall delivered by' a control signal source 26 through the mediumZ of switches 28, 30 and 32'. If desired, the control signal sourcel 28 may be synchronized or related inI it's tim-ing to the timing signals delivered by the timing signal source 34,- whi'chinturn are applied' for triggering the multivibrator circuit.- The switch 36 is shown asproviding means for conditionally operating the control signal source on an independent basis from the timing signal source 34.

It will be understood, therefore, from the simplified block diagram arrangement of Figure l that the timing interval of the pulse perioddefined by the multivibrator upon triggering thereof, may be electrically controlled by means of a control signal upon the closing of one or more of the switchse 28, 30 or 32. By way of eX- ample, if the control waveform illustrated at 38 were applied to the control means 20 through' switch 28, the control means may vbe made to increase the gain of the charging amplifier and hence increase the amplitude' of output signal from the charging amplifier device 10. The effect of the control signal 38 would then be to increase the timing interval of the multivibrator and widenl its output pulse. Contrariwise, should the control means 20, in response to the control pulse 38, be made to reduce the signal delivered by the charging amplifier device 10, the output pulse from the multivibrator would bey narrowed. The control means 22,` on the other hand, could in response to the control signal 38, and upon closingof theswitch 30, be made to either increase or decrease the timing interval of the multivibrator by re` spectively increasing or decreasing the time constant value of the time constant circuit 12. In a like manner,V the control means 24 may be made to operate upon the amplifierdevice 14 in response to the control signal 38 upon4 closing of the switch 32, to either render the amplifer device more or less responsive to the signal deliv-` bodiment ofthe present invention shown in Figure 2.. Here a basic multivibrator circuitbased upon'electron discharge tubes -40 and 42 is shown. Electron discharge tubeH 40 corresponds to the chargingl amplilier device 10 in- Figure 1, while the electron discharge tube 42 corresponds to the ampliiier device 14 ot Figure 1.v rThe time constant circuit comprising the resistor andf 46 corresponds to the time constant circuit 12 of Figure l.. The signal coupling means required-between the output circuit of tube 42 and an input circuit to' tube 40, necessary to permit multivibrator action isprovided by the conductive path 48 between the anode load resistor 50 of tube 42 and the control electrode 51 ofv electron tube 40.

The cathodes Vv52 and v54 of the electron tubes 40 and 42 are connected with a source of negative power supply through resistors 55, 56 and 58,Y respectively. The sourceV of negative power supply may be considered ashaving its i terminal 59 on' a voltage'divider means 60. The capacitor 62- is of su'icient value to maintain the alternatingcurrenty terminal impedance )at point `59 at a suiiiciently low value to maintain good voltage regulating characteristics. Thevoltage divider means is in turn' connected across a potential source having its negative terminal at 64 and its positive terminal connected with circuit ground at 66.

Further considering the Aembodiment of the invention shown in Figure 2, it will be seen that the cathode 52 of electron discharge tube 40 is prevented-trom swinging of the present invention and is described and claimed in United States patent application, Serial No. 343,623, by Arch C. Luther, Ir., entitled Monostable Multi- Vibratloy- 51?@ March 210, 1953. Triggering of the monol stable multivibrator is accomplished by signals delivered by the gate circuit 70 in turn deriving signals from the synchronizing pulse source 72. The gate circuit 70 is assumed to be of a type which will be rendered open to pass signals from the synchronizing pulse source 72 to the screen electrode of tube 42 whenever gate control Voltage is suiciently positivek with respect to circuit ground.

Accordingly, a switching means 76 has been shown which will conditionally apply a positive voltage available at terminal 78 to the gate circuit 70, thereby rendering the gate circuit open into the passage of synchronizing pulses. The negative terminal o f the power supply means whose positive terminal is connected with terminal 78 is indicated as being connected with the grounded terminal 80.

Switch 76, in accordance with the present invention, is also adapted to connect the output terminal of the countdown circuit 82 to the gate circuit in lieu of the positive voltage holding the gate open. In this Waythe gate circuit 70, as more fully described hereinafter, will ybe open only during the delivery by the countdown circuit of a suitable positive going waveform vreferenced with respect to circuit ground.

Control means for the multivibrator circuit of Figure 2, whereby in accordance with the present invention, the timing period or interval of the multivibrator may be changed during operation, includes electron discharge tubes 84, 86, 88, 90 and 92. These electron tubes are adapted to respond to a control signal derived from a Vcontrol signal source 94, which by way of example, has

been shown as timed by signals delivered by the synchronizing pulse source 72. Selective switch means 96 operates to direct the control signal derived from the source 94 to terminals (1, b, c and d of the switch. Terminal a is connected with the control electrode of control tube 86, which in turn is connected in shunt with the cathode resistor 98 of control tube 84. Bias on the control electrode of tube 86 is provided through the agency of resistors 100 and 102 connected in shunt with the negative potential supply having its terminal at 64. The circuit is generally adjusted so that the tube S6 is negatively biased to a point of negligible conduction. Under these conditions, tube 84 employing a common cathode resistor 98 with tube 86 will be held in a condition of minium conduction. Thus, during the period defined by the control signal 104, tube 84 will be` come conducting and will assist tube 40 in delivering a charge to the time constant circuit comprising capacitor 44 and resistor 46. This will in turn produce a longer timing interval for the multivibrator as described in connection with Figure l.

If the armature of switch 96 is connected with the terminal b thereof, the control signal 104 will be ap; plied to the control electrode 106 of control tube 88. If the bias on the control electrode 106 established by the resistor 108 in its connection to terminal 64 is suflcient to maintain the tube 88 in a normally cut oi condition, the positive going control signal 104 will be in a direction to produce conduction in tube 88, thereby bypassing the cathode resistor 54. During such a period the bias on tube 40 will decrease and a greater amplitude of signal will be applied to the time constant circuit 44-46. This in turn will increase the timing interval of the multivibrator.

When the switch 96 is connected to apply control signal to terminal c, control tube 92, normally adjusted to circuit cutoff, will have its control electrode 110 driven in a direction to produce conduction. During the conduction period of the tube 92, the time constant valve of the circuit 44-46 will decrease due to the fact that the overall value of the Vresistance means 46 will be effectively reduced, since a portion thereof is being shunted by the cathode resistor of the electron discharge tube 92. Moreover, bias on the control electrode 112 of tube 42 6 will become more positive during the conduction of the tube 92. BothA of these latter elects will tendl to decrease the timing interval of the multivibrator.

Finally, the application of control pulses to terminal d of the selector switch 96 will tend to drive the control tube into heavier conduction. This will in turn increase the net negative control eelctrode-cathode bias on the tube 42 so as to increase the timing interval of the multivibrator by requiring a greater discharge of the time constant circuit before the conduction of the tube 42 is established.

1f it is assumed that the control signal source 94 derives its control information from thecountdown circuit 82, and that the pulse 104 is of a period' corresponding to two synchronizing pulses, the arrangement of Figure 2 will produce the pulse configurations shown in Figure 3. The synchronizing pulses 114 correspond to the signals delivered by the synchronizing pulse source 72 to the gate circuit 70. With the switch 96 in the a position, it will be assumed that the timing interval of the multivibrator will be such as to produce an output pulse at the upper terminal of resistor 50 corresponding to the pulse 116 in Figure 3b. It is noted that during the period of the control signal 104 shown in Figure 3f, the output pulses 116 are wider than the normal output pulses 118.

Correspondingly, with the switch 96 in the b position, the control tube 88 may be made to operate to increase the duration of the pulses produced by the multivibrator to that shown in Figure 3c. The output pulses 120 are then wider than the previous pulses 116, with the normal duration pulse 118 occurring in the absence of the control signal 104.

With the switch 96 in the c position, the period of the multivibrator timing is reduced so that the output pulses produced thereby may be made to correspond to.4 the pulses 122 of figure d. Here the pulses 122 are much smaller than the normal pulses 118 and are produced only during the period of the control pulse 102. If the control switch 96 is connected to the d position, a pulse widening eect will occur as described hereinabove, so that the resulting output signal would appear smaller to that shown in Figure 3c.

In the operation vof the embodiment of the present invention shown in Figure 2, should the switch 76 be connected with the output terminal of the countdown circuit 82, it will be apparent that the multivibrator will Y be triggered only on alternate synchronizing pulses of the type depicted at 114. The output signal from the multivibrator under such conditions, will then appear as shown on Figure 3d at 124. Modulation of the width of the pulses 124, although not shown in Figure 3e, may be accomplished by the positioning of the switch 96, as described above.

With the above basic principles and operating characteristics of the present invention in mind, consideration will now be given to the manner in which it'may be usefully employed in the generation of the rather complex R. T. M. A. synchronizing and blanking waveform as used in television broadcast. Turning now to Figure 4, there is illustrated a synchronizing signal generator embodying the novel features of the present invention. The synchronizing signal generator comprises a 31.5 kc. master oscillator shown at 128, which may, in accordance with well known practice, be of the crystal type. The signal derived from the masterV oscillator 128 is applied to a countdown chain 130 having a 525:1 countdown ratio, whereby to provide its output terminal 132 sixty cycle information suitable for the control of a vertical blanking generator 134. Output signal from the blanking generator 134 is applied to a blanking mixer Y 136 which is in turn connected with the input circuit of a threshold gate circuit 138. It is the purpose of the threshold gate circuit 138 to clip off all signal excursions above blanking level from the signal delivered by the Wanting meer 136, Output Signal from fheihreshsld e gate 138 is applied to the composite mixer 140 which mixes video` signal from the source 142 with the blanking information. yThe composite mixer 140v also mixes vertical and horizontal synchronizing signal information with the blanking and video signals to form a composite television signal suitable for' application to the television transmitter 143. Horizontal blanking information is provided by the 2:1 countdown circuit 144, acting in cooperation with Vthe monostable multivibrator comprising electron discharge tubes 146 and 148. The form of the multivibrator 146--148 will be recognized as basically the same as that shown in Figure 2. However, the multivibrator 146-148 is provided with a fixed timing interval whereby to define at the output terminal 150 a standard R. T. M. A. horizontal blanking waveform. This waveform is conveyed by the circuit path 151 to the blanking mixer 136 where it is combined with the vertical blanking signal delivered by the vertical blanking generator 134. Due to the action of the threshold gate 138, it is apparent that during the interval when the vertical blanking generator and horizontal blanking generator simultaneously deliver blanking information to the blanking mixer 136, the threshold gate 138 will deliver only vertical blanking infomation to the composite mixer 140. This follows since the horizontal blanking signal will appear to ride on top of the vertical blanking signal and hence be clipped by the threshold gate 138 as described hereinabove.

The basic circuitry of Figure 4 thus far described, is

somewhat conventional in nature. Fundamental considerations involving the overall operation of the synchronizing signal generator, as well as the typical circuitry suitable for use in the elements of Figure 4, are described in an article entitled A synchronizing Signal Generator, appearing in the RCA Review for July 1940, vol. 5, No. 1. United States Patent 2,132,655, to J. P. Smith, entitled System for Producing Electrical Impulses, issued October 11, 1948, is also helpful. Reference to United States Patent 2,223,812, entitled Television System, issued December 3, 1940, to A. V. Bedford describes in detail the requirements of synchronizing waveforms in interlaced television systems, according to R. T. M. A. standards. l. The elements thus far described in connection with Figure 4 may be considered to produce all of the elements of an R. T. M. A. synchronizing signal Waveform, except the horizontal sync, vertical sync, equalizing pulses and vertical pulse serrations.V

Reference to Figure 5a illustrates one vertical synchronizing signal and blanking waveform interval along with adjacent horizontal blanking and synchronizing signal periods of an R. T. M. A. television signal. A detailed discussion of R. T. M. A. standards as to timing of the signal components comprising the standard R T. M. A. television signal is considered in the November 1950 issue of the Proceedings of the I. R. E., page 1253. Briefly, as shown in Figure 5a, the R. T. M. A. synchronizing signal waveform comprises.V horizontal blanking elements such as 152, the vertical blanking intervals such as defined by the period 154, horizontal synchronizing signal waveforms 156, vertical equalizing waveforms such as 158 and vertical serration waveforms 160.

According to the R. T-.-'M. A. standards, the horizontal blanking signal duration is approximately 11;; seconds in duration, with one horizontal line period being approximately 63 me. in duration. The horizontal synchronizing waveform 156 is approximately .08 h. The duration of the double line frequency equalizing pulses 158 Will approximate .04 h. while the duration of the vertical serrations 160 are .07 h. In accordance with the present invention, a single multivibrator is caused to produce the complex horizontal synchronizing signal Waveform and vertical synchronizing signal equalizing pulses and serrations.

The basic multivibrator which is controlled to produce Vs the complex wave generation of the present invention comprises electron discharge tubes 162 and 164. Tube 162 may be considered the charging amplifier device as described in Figure 1^, while tube 164 may be' thought of as the charge responsive amplier device. Tubes 162- and 164 respectively correspond to tubes 40 and 42 of Figure` 2, in their cooperative action to deneV a basic monostable multivibrator circuit. The time constant circuit comprising capacitor 166 and resistor 168 is tailored to cause' the basic multivibrator circuit 162-164 to produce the horizontal synchronizing lsignal waveform der ned by R. T. M. A. standards. able at thev output terminal 170 during the operation of the multivibrator circuit, when triggered at television line f frequency.

in accordance with the presenct invention, the basic multivibrator circuit 162-164 is provided with'contr'ol tubes 172 and 174 for respectively reducing and increasing the Width of the pulse produced by the multivibrator. To understand how this action takes place, it will be' noted that the cathode resistor 176 of electron discharge tubeV 162 is shunted by the series combination of a diode 178 and resistor 180. Control tube 174, on the other hand, shunts the cathode resistor 176 in the degree that the tube 174 is rendered conductive. Control tube 172 is connected with the resistor 180 so that upon suicient conduction of tube 172, the bias developed across resistor 180 will effectively open the diode 178 and remove the shunt across the resistor 176. This, in effect, will increase the cathode load' resistance of tube 162 and result in increased degeneration with less signal drive to the time constant circuit 166-168. As a result, the width of the pulse produced at output terminal 170 will be reduced` whenever control tube 172 becomes suiliciently conductive. In practice, potentiometer 182 may be adjusted to maintain tube 172 at cutoif, except during the control pulse 184, to be discussed hereinafter. The potentiometer 172 is connected across the negative voltage supply having terminals at 186. Control tube 174, however, normally at cutoi due to grid current conduction and charging of the capacitor 188 will increase the timing interval of the multivibrator during control pulse 190 to be discussed later. This etect results from the reduction in the effective cathode load resistance during the charging interval of the time constant circuit 166- 168, thereby chargingthis time constant circuit more heavily. For given acceptance characteristic of the tube 174 it, therefore, follows that the time interval defined by the multivibrator will be widened.

Synchronization of the basic multivibrator circuit 162-164 is accomplished by signals delivered by the front porch delay network 192. The front porch delay network 192 merely delays the 31.5 kc. triggering pulse for the normal interval between the front edge of horizontal blanking and the front edge of horizontal sync in R. T. M. A. television signal. With control tubes 172--174 nonconducting, it will be seen that the multi-V vibrator circuit will have a tendency to be triggered at a 31.5 kc. rate. ance with the present invention, tube 1748 of multivibrator d, the horizontal blanking Waveform generator, is in shunt with tube 168 of multivibrator e, the controllable width multivibrator. Whenever tube 148 is rendered conducting, this will prevent tube 164 normally conducting, from being triggered. Since the multivibrator d is operated at a horizontal line rate, it follows that alternate 31.5 kc. triggering pulses to the multivibrator e will be prevented from affecting or triggering this multivibrator. Thus, as long as the tube 148 of multivibrator e is permitted to shunt tube 164, the controllable multivibrator e, of the present invention, will operate at a 15,750 C. P. S. rate with the time constant circuit 166-168 being tailored to produce a pulse width correi spending to the horizontal synchronizing waveform, as mentioned above.

This signal is avail-j However, it will be observed, in accordl Assuming then the normal condition of multivibrator e to be that of being triggered at the 15,750 C. P. S. rate and producing a pulse width corresponding to the horizontal synchronizing waveform, it follows that the timing interval must be reduced and the triggering rate doubled in order to produce equalizing pulses (see 158, Figure a) While the timing interval must be increased and the triggering rate doubled to produce vertical synchronizing pulse serrations 160 of Figure 5a. This is accomplished in accordance with the present invention, through the novel utilization of a multivibrator chain comprising elements 194, 196 and 198, taken in combination with mixers 200 and 202. For purposes of convenience, these elements have been respectively labeled multivibrators 11, b andfc and mixer o and mixer p, so Athat their corresponding output waveforms may be easily designated in Figure 5. The present invention takes advantage of the fact that the equalizing pulse periods and the vertical sync serration periods of the R. T. M. A.v synchronizing signal shown in Figure 5a are each substantially 3 h. or 3 line periods' long. Since the vertical synchronizing pulse occurs only once every sixtieth of a second, the output signal from the 525:1 countdown chain 130 may be directly connected with the input circuit of the monostable multivibrator a. Multivibrator a may be tailored to produce a pulse 3 h. long, such as 204. Correspondingly, multivibrator 11, driven by multivibrator a may be tailored to produce an output pulse 190, which is substantially 3 h. long. Finally, monostable multivibrator c may be made to produce a pulse 208, which is approximately 3 h. long.

If the output pulses from multivibrator a and multivibrator c are added by mixer o at 200, the resulting output signal 184 may be used to produce conduction in control tube 172 during the first and last 3 h. periods of the vertical synchronizing signal and blanking waveform. Conduction of tube 172 has been shown above to reduce the width of the developed pulse from that of the horizontal synchronizing signal. This reduction may be of such magnitude as to cause the multivibrator e to produce pulses corresponding to equalizing pulses during the rst and last 3 h. period defined by the output signal mixer 0. The waveforms 204 and 208 in Figures 5b and 5c studied in connection with the waveform of Figure 50a, will make this relationship clear.

To produce the vertical sync pulse serrations 160 of Figure 5a, however, the output signal 190 from the monostable multivibrator 196 is applied to the control electrode of tube 174 discussed above. This will increase the period of the pulse produced by the multivibrator e by increasing the charge delivered to the time constant circuit 166-168 as described above. Waveform 190 in Figure Sfc studied in connection with the waveform of Figure 5a will help bring out this relationship.

It will be evident from the description thus far, that one other control function must be exercised at the multivibrator e during the vertical blanking and synchronizing period and that is, it must be permitted to trigger on every 31.5 kc. signal reaching the tube 164. This will permit the equalizing and vertical serration pulses delivered by the multivibrator e to recur at the designated 31.5 kc. rate illustrated in Figure 5a. This may be accomplished in accordance with the present invention by applying a cutoff control signal 210 to the suppressor electrode 212 of the multivibrator d tube 148. This will not interfere with the multivibrator action and timing of the multivibrator 11, but will prevent the tube 148 from appearing as a shunt across the multivibrator tube 164 during periods when tube 148 is conducting. Thus, tube 164 will be effectively triggered on each 31.5 kc. signal only for the duration of the control pulse 210. Control pulse 210 is formed in accordance with the present invention, by adding the signals developed by multivibrators a, b and c, each of-which defines, as described above, a 3 h. period. Thus, the multivibrator 10 will be` caused to operate at a double line frequency rate during the 9 h. period (Figure 5a) corresponding to the equalizing and vertical serration intervals of the R. T. M. A. television signal.

The respective output signals of the multivibrator d, corresponding to the horizontal blanking signalsV 152 are shown in Figure 5e. The output signal of multivibrator e, corresponding to the horizontal sync 156, equalizing pulses 158 and vertical serrations 160, are shown in Figure 5f. The 3 h. and 9 h. pulses, delivered by the mixers o and p respectively, are illustrated in Figures 5g and 5h. The output signal of the vertical blanking generator'134, described hereinabove, is by way of convenience, illustrated in Figure 5i. The blanking interval 154 defined by this pulse is from 14 to 21 h. long.

Finally, the outputsignal from the threshold gate 138y will, of course, appear as shown in Figure 5j, and will comprise only the horizontal blanking intervals 152 and the vertical blanking interval 154.

It is noted that the horizontal blankingsignals do not appear on top of the waveform 154 after the 9 h. period 210, due to the action of threshold gate 138 described above.

It will, therefore, be seen from the above description of the present invention that rather complex electrical waveforms having various pulse durations and pulse repetitionyrates can be synthetized through the control action of a single'multivibrator circuit when constructed in accordance with the present invention. The accuracy of the waveforms thus developed may be extremely high, depending upon the accuracy of the timing waveforms and control waveforms applied `to the `multivibrator. Although particular forms of control waveform generating systems and multivibrator control circuits have been shown, it is to be understood that it is within the scope yof the present invention to employ other means, not

shown, for producing versatile multivibrator control Without departing from the scope of the claims which follow.

What is claimed is:

1. In a monostable multivibrator circuit comprising: a charging amplifier means; a time constant circuit connected in charging relation to said charging amplifier device; a charge responsive amplifier means connected to said time constant circuit; means for maintaining said charge responsive amplifier means normally conducting except in response to a predetermined degree of charge on said time constant circuit; signal coupling means connected in a responsive relation to said charge responsive amplifier and in driving relation to said charging amplilier; means connected to said charging amplifier for maintaining said charging amplifier in a normally non-conductingcondition except in response to signals of predetermined level from said charge responsive amplifier; the combination of means connected to said charging amplifier for varying the amplitude of signal delivered thereby in accordance with an electrical signal; a source of triggering signal connected kto said charge responsive amplifier for timing said multivibrator; a source of control signals bearing a predetermined timing relation to said triggering signals; and signal coupling means connected from said source to said delivered signal amplitude varying means.

2. A monostable multivibrator circuit according to claim l wherein means yare provided for maintaining said control signals in a subharmonic relation to said triggering signals.

3. A monostable multivibrator circuit according to claim l wherein there is additionally provided signal count downk means connected between said source of triggering signal and said charge responsive amplier to trigger said multivibrator a rate lower than said triggering signal recurrence; means connected to said signal count down means for conditionally ineffectuating saidy count down action in response to electrical signals such to realize triggering at saidV triggering signal rate; and

a source of trigger rate controlsignals connected toy said count down circuit ineffectu'ating means.

4. A monostable multivibrator circuit according to claim 3 wherein means are provided for maintaining said trigger rate control signais in a predetermined timing relation to said triggering signals. Y

5. ln a monostable multivibrator circuit, the combination of: a charging amplifier means; a time constant circuit connected in charging relation to said charging amplifier means; signalk responsive means connected' to said charging amplifier meansl to control the amount of charge conditionally applied to said time constant circuit by said charging amplifier means; a charge responsive amplifier means connected in responsive relation to said time constant circuit; means for maintaining said charge responsive amplifier normally conducting except in response to a predetermined degree of charge on said time constant circuit; signal coupling meansl connected etween said charge responsive amplifier means and said charging-amplifier means to drive said charging amplifier means by signals delivered by said charge responsive amplifier means; means connected to said charging amplifierA means for substantially disabling said charging amplifier means except'in response to driving signals in excess of 'a predetermined level from said charge responsive amplifier means; a source of triggering signal connected to` said charge responsive amplifier means for triggering said multivibrator; a source of control signals bearing a predetermined timing relation to said triggering signals; and signal coupling means connected from said last named means to said charging amplifier means charge delivering control means.

6. In a monostable multivibrator circuit, the combination of: a charging amplifier means; a time constant circuit connected in charging relation to said charging amplitier means; a charge responsive amplifier means connected in responsive relation to said time constant circuit; signal responsive means connected to said charge responsive amplifier means to control the degree of respouse of said charge responsive amplifier means to a given charge in said time constant circuit; signal coupling means connected between said charge responsive amplitier means and said charging amplifier means to drive said charging amplifier means by signals delivered by said charge responsive amplifier means; means connected to said charging amplifier means for substantially disabling said charging amplifier means except in response to driving signals in excess of a predetermined level from said charge responsive amplifier means; a source of triggering signal connected to said charge responsive amplifier `means for triggeringsaid multivibrator; a source of control signals bearing a predetermined timing relation to said triggering signals; and signal coupling means connected from said last named means to said response control means for said charge responsive `amplifier means. 7. In a television waveform generating system for producing a complex signal comprising a line timing lcomponent, a field equalizing component, a field serration component, and a field blanking component, the combination of: a signal generating means producing a'base signal harmonically related to the desired frequency of said line timing pulse component; a multivibrator circuit; means coupled "to said signal generating lmeans and said multivibrator for triggering said multivibrator with signals derived from said signal generating means; signal responsive means coupled to said multivibrator for controlling the frequency of operation of said multivibrator; signal responsive means coupled to said multivibrator for varying the timing interval defined by said multivibrator; means coupled to said signal generating means for developing frequency control signals in time correspondence to conditional transitions in said television waveform between line timing components and frame blanking components; means applying said frequency control signals to said multivibrator frequency controlling means for control thereof; means coupled' to said signal generating means for developing timingV control signals corresponding in time 'toY atleast periods coincident with said transition between said line timing and field" equalizingl components; and means applying said timing control' signal to said timing intervalvarying means;

8. A television waveform generating system according p to claim 7, wherein said multivibrator frequency Acontrolmeans comprises a means coupled with said multivibrator`- for conditionally disabling said multivibrator andwherein" said frequency control signal developingmeans comprises a signal countdown system so that said frequency` control' signal is subharmonically related to said base signal generating means. y f

9. A television waveform generating system' according to claim 7, wherein multivibrator comprises: a` chargingJr amplifier; a time constant circuit connected to said charging amplifier for charging thereby; a charge responsive" ponent, a field equalizing component and a eld serration component, said equalizing and serration components being adjacent one another in a group of a first,.

second and third consecutive fieldperiods falling within` said field blanking period; said equalizing components` occupying said rst and third field periods, the combinatiori'of:l *aV signal generating means producing a base signal having a recurrence frequency of twice the desired frequency of said line timing component; signal countdown means coupled to said signal generating means forv producing a vertical field timing signal corresponding to the frequency of said field blanking component; a-pulse chain generating means coupled to said last named mea-ns for generating first, second and third-timing pulses respectively equal in duration to said first .field periodi equalizing component, said field serration component and said third field period equalizing component; a monostable multivibrator circuit, having a normal timing interval; equal to individual line timing signals; means coupled to said signal generating means and said` multivibrator' for triggering said multivibrator with. signals derived' from said base signal generating means; signal responsive means coupled between said multivibrator andL said pulse` chain generating means for causing said multivibrator to exhibit a timing interval equal to individual equalizing` signals during said first and third field periods; signal responsive means coupled between said. multivibrator and said pulse chain generating means for causing said multivibrator to exhibit a timingr interval equal to individual serrations comprising said field serration component; sig-` nal countdown means coupled to said base signal generator for producing line frequency signals; means connected between said last named means and said multivibrator for conditionally desensitizing said multivibrator from trig-` gering by said base signal generator on alternate base signal generator signal; means coupled to said pulse` chain generating means for effectively combining said` first, second and third timing pulses to form a count control pulse; and means coupled between said last named means and said desensizing means for conditionally rendering said desensitizing means of non-effect during. said count control pulse.

1l. I n a television transmitting terminaLmeans to generate a train of pulses including a first series of pulses` of one width followed by a second series of pulsesfof another width, comprising, a monostable multivibrator'- having first-and second amplifying circuits cross-coupled so that a stable condition exists when the first amplifying circuit is nonconductive and the second amplifying cir-4 13 cuit is conductive, said multivibrator having an output terminal, a source of synchronizing pulses coupled to said multivibrator to periodically trigger the multivibrator from said stable state to the timed state wherein the first amplifying circuit is conductive and the second amplifying circuit is non-conductive for a predetermined time duration, whereby said rst series of pulses of one width is generated at said output terminal, a source of control pulses each having a duration equal to the duration ,of said second series of desired output pulses of another Width, and means coupling said control pulse source to only said multivibrator irst amplifying circuit to change the durations of said timed states, whereby said second series of pulses of another width is generated at said output terminal.

12. In a television transmitting terminal, means to generate a train of pulses including a rst series of pulses of one width followed by a second series of pulses of another width, comprising, a monostable multivibrator having rst and second amplifying circuits cross-coupled so that a stable condition exists when the first amplifying circuit is non-conductive and the second amplifying circuit is conductive, said multivibrator having an output terminal, a source of synchronizing pulses coupled to said multivibrator to periodically trigger the multivibrator from said stable state to the timed state wherein the irst amplifying circuit is conductive and the second amplifying circuit is non-conductive for a predetermined time duration, whereby said iirst series of pulses of one width is generated at said output terminal, a source of control pulses each having a duration equal to the duration of said second series of desired output pulses of another width, a synchronizing coupling from said synchronizing pulse source to said control pulse source, and a third amplifying circuit having an -input coupled to said control pulse source and having an output coupled to only said multivibrator rst amplifying circuit to change the durations of said timed states, whereby said second series of pulses is generated at said output terminal.

References Cited in the tile of this patent UNITED STATES PATENTS Gray June l2, 1956 

